Electrophoretic imaging apparatus including means to project an imageat a liquid nip

ABSTRACT

A PHOTOELECTROPHORETIC IMAGING SYSTEM AND APPARATUS ARE DESCRIBED WITHIN ELECTRICALLY PHOTOSENSITIVE PARTICLES DISPERSED IN A CARRIER LIQUID ARE SUBJECTED TO AN ELECTRIC FIELD AND EXPOSED TO IMAGEWISE LIGHT CAUSING SELECTIVE PARTICLE MAGRATION IN IMAGE CONFIGURATION. THE IMAGEWISE EXPOSURE IS DIRECTED AT A LIQUID NIP OF THE PARTICLE-LIQUID SUSPENSION. THE EXPOSURE IS NOT DIRECTED THROUGH EITHER NIP FORMING SURFACE.

March 27, 1973 J. w. WEIGL 3,723,283

ELECTROPHORETIC IMAGING APPARATUS INCLUDING MEANS To PROJECT AN IMAGE ATA LIQUID NIP Filed Jan. 6, 1971 INVENTOR. JOHN W WEIGL BY/ w A T TORNE VUnited States Patent 3,723,288 ELECTROPHORETIC IMAGING APPARATUS IN-CLUDING MEANS T0 PROJECT AN IMAGE AT A LIQUID NIP John W. Weigl, WestWebster, N.Y., assignor to Xerox Corporation, Stamford, Conn.Continuation-impart of application Ser. No. 760,311, Sept. 17, 1968.This application Jan. 6, 1971, Ser.

Int. Cl. BOlk 5/02 US. Cl. 204300 5 Claims ABSTRACT OF THE DISCLOSURE Aphotoelectrophoretic imaging system and apparatus are described whereinelectrically photosensitive particles dispersed in a carrier liquid aresubjected to an electric field and exposed to imagewise light causingselective particle migration in image configuration. The imagewiseexposure is directed at a liquid nip of the particle-liquid suspension.The exposure is not directed through either nip forming surface.

BACKGROUND OF THE INVENTION This invention relates in general to imagingsystems. More specifically, the invention concerns aphotoelectrophoretic imaging system. This application is acontinuation-in-part of my copending application Ser. No. 760,311 filedSept. 17, 1968, now Pat. No. 3,616,390, in the United States PatentOfiice.

There has been recently developed an electrophoretic imaging systemcapable of producing color images which utilizes an imaging suspensionof electrically photosensitive particles in a liquid insulator. Thisprocess is described in detail and claimed in US. Pats. 3,384,566 to H.E. Clark, 3,384,565 to V. Tulagin et a1. and 3,383,993 to Shu-HsiungYeh. The suspension is placed between electrodes, one of which isgenerally conductive, called the injecting electrode and the other ofwhich is generally insulating and called the blocking electrode. One ofthese electrodes is at least partially transparent to activatingelectromagnetic radiation. The suspension is subjected to a potentialdifierence between the electrodes and exposed to an image through atransparent electrode. As these steps are completed, selective particlemigration taken place in image configuration, providing a visible imageat one or both of the electrodes. The suspended particles must beelectrically photosensitive and apparently undergo a net change incharge polarity upon light exposure when brought into interaction rangeof an electrode. In a monochromatic system, particles of a single colormay be used, producing a single colored image equivalent to conventionalblack-and-white photography. In a polychromatic system, the images areproduced in natural color because mixtures of particles of two or moredifferent colors which are each sensitive to light of a specificwavelength or narrow range of wavelengths are used.

This system, using preferably a transparent conductive injectingelectrode, a substantially insulating blocking electrode andphotosensitive particles dispersed in an insulating carrier liquidbetween the electrodes has been found to be capable of producingexcellent images. One major disadvantage in the prior art systems asshown by the patents listed above is that the transparent conductiveelectrode had to be at least as large as the final image to be produced.This requires that expensive and usually fragile electrode materialsmust be used. Typically, NESA glass, a tin oxide coated glass availablefrom Pittsburgh Plate Glass Co., was used as the injecting electrode. Inaddition, these electrodes because of their transparency,

ice

cost and fragility required that the image formed on their surface betransferred to another member so that the electrode could be reused. Thetransfer and subsequent cleaning steps represent additional, unnecessayprocess steps. If the cleaning step is not efiicient subsequent imageswould be marred. In addition, the cleaning step tends to abrade thesurface of the injecting electrode afiecting the optical clarity of thatmember. Where the injecting electrode is in the form of a cylinder theimage is projected down the axis of the cylinder and is reflected by amirror into the imaging zone requiring a more complex optical system.

SUMMARY OF THE INVENTION It is, therefore, an object of this inventionto provide a photoelectrophoretic imaging system which overcomes theabove-noted disadvantages.

It is another object of this invention to provide a photoelectrophoreticimaging system which does not require the use of relatively largeconductive transparent electrodes.

It is another object of this invention to provide a relatively simplephotoelectrophoretic imaging system.

It is another object of this invention to provide novelphotoelectrophoretic imaging apparatus.

The above objects and others are accomplished in accordance with thisinvention by providing a photoelectrophoretic imaging system in which animaging suspension comprising electrically photosensitve partclesdispersed in a carrier liquid is caused to form a sharply defined liquidnip between electrodes or in an electrical field, exposed to imagewiseactinic electromagnetic radiation close to the nips; the radiation andfield causing selective particle migration in image configuration. It ispreferred that the liquid nip between the electrodes be as small aspractical so that light may penetrate the normally dark colored imagingsuspension to the point where the electrical field is sufiicient tocause particle migration. It is therefore preferred to use sharp-edgedobjects, or small diameter rollers or tubes as the nip forming member.Preferably, the space between the surfaces containing the nip will beone mil or less.

Preferably, the imaging suspension is coated on the surface of aconductive flexible web which passes over one of the nip formingmembers, the imaging suspension then being contacted by an insulatingweb which passes between the imaging suspension and the opposite nipformer, at which point imagewise exposure and field application occur.Alternatively, the liquid suspension could be provided on the surface ofthe insulating Web. The imaging suspension could also be provided on oneof the webs as a dry mixture of particles in a binder and the binderliquified by heating or solvent application just prior to imaging. Onseparation of the webs after imaging a positive image will be formed onone web and a negative image formed on the other. It is also possible tohave both webs insulating with a corona charge applied to the back ofeither or both webs to supply the field. Assume, for example, that acharge is applied to the back of one web and the imaging suspension iscoated on the opposite web, as the webs are brought into the imagingzone the web carrying the suspension would pass over a grounded rollerwhich would provide the requisite electric field across the imagingsuspension.

The webs may also both be conductive and the field applied between theconductive webs if the webs are separated immediately after exposure tominimize particle oscillation between webs.

Since the conductive web need be conductive only at the time of imagingthe web could be photoconductive, for example, a pre-illuminatedoxide-binder coating on a conductive substrate. The zinc oxide coatingwould be sufficiently pre-illuminated so that it would remain conductivefor a time sufficient to move into and out of the imaging zone.

Where an insulating flexible web is used the insulating material maycomprise any suitable material. Typical insulating materials include;paper, baryta paper, polyethylene coated paper, cellulose acetate, nitrocellulose, polystyrene, polyvinylfluoride, polyethylene terephthalateand mixtures thereof. Where the image is transferred apolytetrafluoroethylene clad polyvinyl fluoride is preferred because itcombines the ease of cleaning of the former with the high dielectricconstant of the latter. Where the image is not transferred a zincoxide-binder layer is preferred because its conductivity and brightnessare readily controlled.

The conductive flexible web, where applicable, may consist of anysuitable material. Typical materials include; flexible webs of aluminum,steel, brass, copper, nickel, zinc or similar coatings on plastic films,cloth, or paper rendered conductive by inclusion of a suitable materialtherein. Glass cloth impregnated with a carbon-loaded sinteredpolytetrafluoroethylene composition is preferred because it combinesflexibility with conductivity and ease of cleaning.

The imaging suspension may comprise any suitable electricallyphotosensitive particles dispersed in a carrier liquid; these particlesmay be of one color to produce monochrome images or may be mixtures oftwo or more colors, for example, cyan particles, yellow particles andmagenta particles mixed together in a suspension. Typical electricallyphotosensitive particles and carrier liquids are disclosed in U.S. Pat.3,384,488, issued May 21, 1965 to V. Tulagin et al., and US. Pat.3,357,989, issued Dec. 12, 1967 to I. F. Byrne et al., the disclosuresof which are incorporated herein by reference.

The imaging suspension may be applied to either or both webs by anysuitable method. Typical methods include dip coating, spraying, orbrushing. The suspension typically contains a dielectric liquid anddissolved resins and other additives to stabilize the suspension and toact as image fixing aids. The suspension may also be coated on a member,dried then liquified prior to imaging by heat or solvent application.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages of this improved methodof photoelectrophoretic imaging will become apparent upon considerationof the detailed disclosure of the invention especially when taken inconjunction with the accompanying drawings wherein:

FIG. 1 is a side sectional view of a simple exemplaryphotoelectrophoretic imaging system wherein both webs are reused and theimaging suspension is applied to a conductive web.

FIG. 2 is a side sectional view of a simple exemplaryphotoelectrophoretic imaging system wherein a conductive electrode webis used as the final image bearing sheet and the imaging suspension isapplied to an insulating surface.

Referring now to FIG. 1, insulating web 1 is entrained over conductiveroller 3 which is connected to a source of DC potential, not shown, anddrum 5 which is partially submerged in cleaning bath 7 held in reservoir9. To aid cleaning, bath 7 may be agitated, for example ultrasonically,and an electrode could be placed in the bath to aid particle removal.

Conductive web 11 is entrained over conductive roller 12, connected to asource of DC. potential not shown, transfer roller 13 and drum 14. Theimaging suspension 15 held in reservoir 16 is supplied to web 11 by feedroller 17.

In operation conductive web 11 picks up imaging suspension 15 from feedroller 17. The web then moves to a point where insulating web 1 contactsthe imaging suspension forming a liquid nip at the imaging station 19.The liquid nip is exposed to image-Wise electromagnetic radiation 20whch in this exemplary instance is a light image projected by slitprojection means 23 from a moving document 24 which is to be copied.Light shield 25 is provided to eliminate stray illumination. Applicatonof field between rollers 3 and 12 combined with imagewise exposure 20causes particle migration in image configuration with a positive imagenormally adhering to conductive web 11. This image is then transferredto receiver sheet 27 by pressure or electrostatic transfer. Receiversheet 27 is entrained over guide roller 29. The image may then be fixedby heat or laminated by overcoating or other suitable fixing method.

Insulating web 1 is directed into cleaning bath 7 where unwanted pigmentparticles are removed before returnto imaging station 19.

Referring now to FIG. 2, conductive web 31 is provided in roll form andpasses over conductive roller 32. Roller 33, comprising conductivecentral core 34 overcoated with insulating material 35, and roller 32are connected to a source of DC. potential not shown.

In operation imaging suspension 37 held in reservoir 38 is supplied byfeed roller 39 to roller 33. The imaging suspension is then contacted byweb 31 creating a liquid nip at imaging station 40 where it is exposedto imagewise electromagnetic radiation 43 which in this exemplaryinstance is light projected by projection means 44 from the movingtransparency 45 which is to be copied. Alternatively, the light may belight reflected from an opaque document. Light shield 46 protects theimaging station from stray illumination. The combination of field andimagewise light cause particle migration in image configuration with apositive image being formed on web 31. This image may then be vieweddirectly or fixed as discussed above.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following examples furtherspecifically illustrate the improved photoelectrophoretic imaging systemof this invention. Parts and percentages are by weight unless otherwiseindicated. The examples below are intended to illustrate variouspreferred embodiments of the present invention. All of the followingexamples are carried out in an apparatus of the general type illustratedin FIG. 2 with additional means not shown to clean particles from thesurface of roller 33. A 3000 K. tungsten-iodine lamp is used to providethe illumination. The light image is projected by the lens systemdescribed in US. Pat. No. 3,212,417, issued Oct. 19, 1965 to Gundlach.In this case imagewise light is projected and directed at the liquidnip.

EXAMPLES I In this example the drum is made conductive and the imagebearing member is insulating.

A web of zinc oxide coated paper provided in roll form is entrained overa A; inch conductive rubber roller. A three-inch diameter aluminum drumis used as the injecting electrode.

The coated paper web is positioned so that it is pressed lightly againstthe aluminum drum. An imaging suspension, prepared by dispersing sevenparts of the x form of metal free phthalocyanine prepared as shown inUS. Pat. 3,357,989 in parts of kerosene and 10 parts tricresyl phosphateis coated on the surface of the aluminum drum to a thickness of aboutone mil. The positive terminal of a 3000-v. DC. potential source isconnected to the conductive rubber roller and the negative terminal isconnected to the aluminum drum. The rubber roller and aluminum drum aredriven by motors so that there is little relative movement between theimaging suspension and the aluminum drum. The imaging suspension ismoved through the imaging zone at about 50 formed on the surface of thezinc oxide paper.

EXAMPLE II In Examples II and III the drum is made insulating and theimage bearing member is conductive.

A web of aluminized Mylar provided in roll form is entrained over a inchdiameter conductive rubber roller with the conductive side out. Ablocking electrode is made by attaching a sheet of Teflon coated tedlarto the surface of a three inch diameter aluminum drum. The blockingelectrode is positioned so that it is pressed lightly against thealuminized surface of the aluminized Mylar web. An imaging suspension ismade up as in Example I. The imaging suspension is coated onto theblocking electrode surface to a thickness of about 1 mil. The positiveterminal of a 3,000-volt DC. potential source is connected to thealuminized surface of the web, the negative terminal being connected tothe conductive center core of the blocking electrode. The blockingelectrode and conductive side roller electrode are driven by a motor sothat there is little or no relative movement between the imagingsuspension and the aluminized Mylar as they move through the imagingzone. The imaging suspension and Mylar sheet pass through the imagingzone at about 50 cm./ sec. while the liquid nip is exposed to animagewise light source of about 200 foot candles. As the aluminizedMylar is moved out of the nip a positive, blue image is found adheringto the aluminum surface of the aluminized Mylar.

EXAMPLE III The experiment of Example II is repeated except that theimaging suspension comprises 2 parts Monolite Fast Blue 6.8., the alphaform of metal free phthalocyanine, 2 parts Watchung Red B (a magenta azopigment) and 2 parts 2-pyridyl-8,13-dioxodinaphtho-(2, l-b; 2', 3'-d)-furan-6-carboxamide, prepared by the method disclosed in copendingapplication Ser. No, 421,281 filed Dec. 28, 1964, now Pat. No.3,447,922, in 100 part of Sohio Odorless Solvent 3440. The roller speedsare adjusted to 4 cm./sec. and the exposure is adjusted to 2,000 footcandles. The exposure is made through a full color Kodachrometransparency. A fully color image is produced on the aluminum surface ofthe aluminized Mylar sheet.

Although specific components and proportions have been described in theabove examples, other suitable materials, as listed above, may be usedwith similar results. In addition, other materials may be added to theimaging suspension or electrically photosensitive particles tosynergize, enchance or otherwise modify their properties. For example,the photosensitive particles may be charge transfer sensitized to altertheir electrical response.

Other modifications and ramifications of the present in vention willoccur to those skilled in the art upon a reading of the presentdisclosure. These are intended to be included within the scope of theinvention.

What is claimed is:

1. An apparatus for photoelectrophoretic imaging which comprises:

(a) at least two nip forming members spaced up to about one mil forforming a nip;

(b) a source of DC. potential for applying an electrical field acrosssaid nip;

(c) projection means; and,

(d) means to position said projection means for directing imagewiseelectromagnetic radiation to said nip other than through a nip formingmember.

2. The apparatus of claim 1 wherein at least one of said nip formingmembers comprises a flexible web entrained over a roller electrode.

3. The apparatus of claim 1 wherein at least one of said nip formingmembers comprises a conductive material.

4. The apparatus of claim 1 wherein at least one of said nip formingmembers comprises a photoconductive insulating material.

5. The apparatus of claim 1 including means for applying a liquidimaging suspension to at least one of said nip forming members.-

References Cited UNITED STATES PATENTS 9/1969 Waly 96l.3

JOHN H. MACK, Primary Examiner W. I. SOLOMON, Assistant Examiner US. 01.X.R. 355-3, 4

